Poly(dimethylsiloxane) (PDMS) is an ideal stamp material for microfluidic devices and microcontact printing due to its elastic characteristics and ease of handling. However, PDMS suffers from an essential drawback. Because the surface is hydrophobic, using these materials with aqueous solutions has inherent problems due to the mismatch in polarities. For this reason, most microcontact printings techniques are restricted to the application of nonpolar inks, such as alkanethiols. Also, many microfluidic devices constructed from this material require active pumping to move the fluid through the hydrophobic channels. In response to such problems, attempts have been made to fabricate PDMS with a hydrophilic surface. For instance, PDMS has been rendered hydrophilic with an O2-based plasma before inking them with a solution containing polar molecules. Unfortunately, however, plasma treatment generates a layer on the surface of the stamp that is unstable and brittle. Attempts have also been made to graft hydrophilic monomers onto the surface of the PDMS elastomer. For example, U.S. Patent Application Publication No. 2002/0098364 to Bernard, et al. describes a method in which the surface of a PDMS elastomer is grafted with a hydrophilic monomer. Such a graft polymerization technique, however, requires multiple reaction steps and is thus inefficient and costly to practice.
As such, a need currently exists for an improved technique for forming a silicone elastomer that possesses hydrophilic properties.